Process and apparatus for drying colloidal substances such as lignite



W. F. SCHUSTER PROCESS AND APPARATUS FOR DRYING COLLOIDAL Nov. 7, 1961 SUBSTANCES SUCH AS LIGNITE 5 Sheets-Sheet 1 Filed Jan. 20, 1958 Fig.3

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Nov. 7, 1961 w. F. SCHUSTER PROCESS AND APPARATUS FOR DRYING COLLOIDAL SUBSTANCES SUCH AS LIGNITE 5 Sheets-Sheet 5 Filed Jan. 20, 1958 pressurized hot water pressure steam INVENTOR WILHELM F. SCHUSTER BY 3 1 SWIQAM+H mo RN lays United States Patent 3,007,254 PROCESS AND APPARATUS FOR DRYING COL- LOIDAL SUBSTANCES SUCH AS LIGNITE Wilhelm F. Schuster, Leoben, Steiermark, Austria (W eyrgasse 7/7, Vienna 40/ III, Austria) Filed Jan. 20, 1958, Ser. No. 710,097 Claims priority, application Austria Aug. 10, 1953 p 8 Claims. (Cl. 34-13) This invention concerns improvements in a process for drying colloidal substances, such as lumpy lignite, in which the substance after being charged into a closed pressure vessel, called a steamer or steaming vessel, is first heated up by hot Water and pressure steam to about 200 C. and subsequently cooled by pressure relief and release of steam. During heating up, about 50 percent of the water content exudes in liquid form from the coal due to a partial destruction'of its colloidal structure, and a further percentage ofwater boils otf during the subsequent pressure relief. With a given initial structure and water content of the charged material, the total percentage of water removed is dependent only on the peak temperature employed. Through the use of hot water and condensing pressurized steam as the heating medium, a deteriorating decomposition of the coal particles is avoided, as is invariably bound to occur under normal hot gas drying conditions where the dry heat continues to cause the particle surfaces to desiocate, shrink and spall oif to eventual disintegration. This arises from the fact that, due to the action of the hot gases and/or radiating heat, the boiling point at atmospheric pressure of the water in the coal is exceeded, causing immediate volatilization. Since great amounts or heat are required for vaporization, the radiated heat will not penetrate deeply at first, but rather the surface layers of the lumps will desiccate and shrink, radial cracks will appear, and then a layer will spell E, exposing the next layer to this progressive disintegration action until the whole lump of coal is eventually disintegrated.

For about thirty years, this well-known drying process has been applied in a manner in which the steam released from a hot steamer was piped into an identical cold steamer charged with raw coal, and in which additional quantities of live steam from extraneous sources were used to attain the required high temperature level. In this method, high temperature heat was directly transferred to the cold charge, a procedure which, apart from the detrimental shock effect on the texture of the material, constituted poor heat economy, since at about 120 C., equalization of pressure and temperature would occur between the two steamers, with the result that the balance of heat left over in the hot steamer was wasted.

The present invention is based on the finding that for cold steamer and raw material charge heat-up, about the same amount of heat is required as that liberated during cooling the hot steamer, and that the process may, therefore, be sustained with a minimum input of ex traneous heat, provided the liberated heat from the hot steamer is transferred, with insignificant losses of sensible heat and heat potential, to a cold charged steamer in such a manner that high temperature and low temperture quantities of heat as released from the hot steamer are introduced, respectively, to high preheat and low preheat portions of the raw material charge resting in the cold steamer. This type of selected heat transfer, while impossible to achieve by direct transfer from a hot to a cold steamer, has been realized by the present invention by arranging for multi-stage cooling and heat-up stages in such a manner that the heat transferred froma hot steamer at different temperature levels in successive cooling stages is stored up in a corresponding number of accumulators, from where it is, after a convenient interval of time, admitted to a cold steamer in the reverse order of cooling, that is with the coolest accumulator delivering its heat first into the lowest heating stage of the cold steamer.

A plant incorporating the essentials of the invention may basically consist of one steamer only and the required set of heat accumulators. In this set-up, additional live steam will only be used to provide the heat required for the topmost, or hot-test, heat-up stage. This shows that the extra heat requirement will decrease with an increased number of stages. Taking account of unavoidable heat losses, the preferable set-up for a temperature range of from 0-200 C. would for simplicity of design, operate with from 3 to 5 heat transfer stages. In the case of a large size plant, several identically built steamers can be served by one and the same set of staged heat accumulators, a feature which will entail a proportional reduction of both plant outlay and heat loss. Yet, for economic reasons, the accumulators should he of ample capacity, such as 76 m. as indicated in the accompanying table, item 2, which would make the accumulator capable of allowing 1 kilogram of pressurized hot water to receive 10 kilocalories of heat, so as to avoid major fluctu-' ations of pressure and temperature during operations. In addition to substantial savings in heat cost, the accumulators permit a great flexibility of operations, in that individual steamers can be operated independently, each steamer can be taken out of production for repairs without interfering with the overall schedule, and in that the number of steamers operating can be adapted to suit given market and sales conditions. Further, the accumulators permit an optimal timing of individual phases of the process, thus making for optimum results. Another important advantage of multistage operation lies in the conservation of the particle sizes of the raw material during the heat-up stages due to the absence of excessively steep temperature gradients between the heating medium and the charged raw material.

However, the use of this stage accumulator method is unavoidably bound to certain basic requirements. Despite the fact that the method uses small temperature gradients, the raw material heat-up must be necessarily fast for practical reasons, and this can be achieved by charging the raw material as a loosely packed column in the steamer. If, for economic reasons, run-of-the-mine lignite that may contain large amounts of fines and clay is left in this state and as such charged for drying into the steamers, this loose but fairly compactly charged column will bake into an almost impermeable mass by the cementing efiect of the Water-softened clayey impurities. During the pressure relief which follows the heat-up cycle, large amounts of fines would be entrained in the exhaust steam and cause serious trouble everywhere in the system. This is eliminated in the invention by a washing operation, in which hot water originating from the process is caused to flow upward through the material charge, thereby washing, flufling and preheating the coal. On discharge from the steamer the first cool and mud-laden portion of the preheat water is piped 01f, while the cleaner and hotter portions that follow Will be bypassed, heated up by low pressure steam, and re-circulated through the steamer charge until the desired level of coal preheat has been reached.

In connection with this washing operation, it should be noted that the Walls of the steamer, which can give off their heat content by convection and radiation only, are very sluggish in giving off their heat during the pressure-relief period so that, even after the steamer has been discharged and refilled, the walls will show temperatures varying from 140 to 150 C. To avoid wasting this amount of heat into the lower-temperature water during the washing operation of the next operating cycle, the invention provides for continuous sprinkling of the interior wall surfaces of the steamer throughout the pressure relief period by circulating condensate by a circulating pump and delivering the recovered wall heat in the form of steam to the proper stage accumulators.

Under carbonizing conditions prevailing during the steaming period, amounts of carbon dioxide are formed which, remaining unaffected by condensation and evaporation, would, by re-circulation, attain a degree of concentration suflicient to arrest the process prematurely. According to the invention, the carbon dioxide, collected in high concentration in the lower sections of the steamers and mixed with a certain quantity of steam, is passed through surface heat-exchangers incorporated in the accumulators. In passing through, this compressed mixture gives off its sensible heat and is subsequently discharged into the atmosphere through a relief valve.

In the process described so far, hot water and saturated steam are used exclusively and the drying effect for a given type of coal is essentially dependent on the pressure and temperature peak of the live steam input.

In this way, however, very high drying effects cannot be achieved, since peak temperatures would have to be used of such order that the structure of the coal particles would not be able to withstand them. If higher drying effects were desired much thicker walled steamers would be required, which would have a decisive etfect on both cost of plant and operation. On the other hand, it has been established by extensive investigations that a coal, well pre-treated with saturated steam, will readily withstand the action of moderately superheated steam without incurring particle decomposition or loss of resistance to particle decomposition during the subsequent pressure relief boiling-elf phase of the drying operation. Thus, the invention provides, that following the saturated steam treatment, moderately superheated steam is passed through the material charge in order to supplement the restricted primary exudation of colloidal water by a secondary boil-off treatment over any desired length of time. To achieve this, steam is circulated by means of a suitable blower and, according to the invention, is held at a temperature of about 240 C. by being passed through a high pressure steam-heated superheater which positively eliminates any occurrence of excessively high circulating steam temperatures. The boil-off steam which arises from drying the material charge with superheated steam is stored and reused in a new heat-up operation at any convenient time. After heating with superheated steam, the steamers are pressure relieved in stages as in the saturated steam operation.

The superheated steam process becomes most economical when the coal is made to boil off the total quantity of steam required to sustain the process, that is, to provide the extra amount of heat otherwise supplied from extraneous sources. This feature would appear most attractive for locations where the availability of water constitutes aserious problem.

The coal treated by this process, in contrast to the coal treated by the prior art processes, is thus made considerably drier and cleaner while substantially retaining its shape and strength characteristics.

The means by which the objects of the invention are obtained are disclosed more fully with reference to the accompanying drawings, in which:

FIGURE 1 is a diagram showing the prior art heat flow from a hot to a cold steamer;

FIGURE 2 is a diagram showing a theoretical pattern of ideal heat flow;

FIGURE 3 is a diagram presenting the heat flow pattern obtained when using the intermediate stage accumulators according to the invention;

FIGURE 4 is a diagram comparing saturated steam drying with saturated steam-superheated steam drying with xylite coal as the raw material;

FIGURE 5 is a diagram showing the heat flow when drying with saturated steam exclusively;

FIGURE 6 is a diagram presenting the fiow when drying with saturated steam and superheated steam;

FIGURE 7 is a schematic layout of a commercial drying installation operated on the saturated steam process;

' FIGURE 8 is a schematic layout of a commercial drying installation operated on the saturated steam-superheated steam process;

FIGURE 9 is a section of a steamer and receiver unit in larger scale; and

FIGURE 10 is a section through a steam accumulator in larger scale.

In FIGURE 1, representing the prior art, the total heat content of a hot steamer A, heated up to a peak temperature of 220 C., is indicated by the left-hand rectangle with subdivisions a through h, denominating subquantities of heat whose temperature limits are seen from the left-hand graduation. The right-hand rectangle represents in analogous manner a cold steamer B awaiting heat-up. Prior to this invention, heat transfer from steamer A to steamer B was in the sense of the arrows pointing from A to B. This prior art permits the recovery of the heat subquantities from subdivisions a, b, c and d only, Whereas the heat subquantities from the boldlined subdivisions e through h are lost. This loss is reflected in the heat requirement of a magnitude as indicated by subdivisions e through 11' of the cold steamer B. This heat requirement must be made up by live steam input.

Inan analogous manner, FIGURE 2 shows the heat flow from a steamer C to a steamer D; while this pattern would represent the ideal case, it is fundamentally impossible to achieve by direct transfer of heat from one steamer into another. In a further analogous presentation, FIGURE 3 shows the heat flow between steamers C and D with intermediate accumulators according to the invention. It will be noted that the subquantities a through g are, in this same order, transferred from steamer C into the coordinated accumulators S through S from which, at any time, the same subquantities of heat can be fed in reverse order into the subdivisions g through a of steamer D. The subquantity It cannot be transferred and is lost, while the subquantity h must be made up by live steam. A comparison of FIGURES l and 3 for required heat input clearly shows the savings that can be achieved by using the process schematically depicted in FIGURE 3.

In FIGURE 4, for example, the extraction of water, expressed in percent moisture contained in the raw charge material, in this case xylite coal, is plotted against the temperatures and pressures employed during the drying period under the saturated steam process and the saturated steam-superheated steam process, respectively. According to this graph, saturated steam drying generally follows a course indicated by the line ikl--m--n- --p, with pressure and temperature reaching peaks of about 24 atmospheres absolute and 220 C. at point m, and attains at point p a final water content in the dried coal which is equivalent to 18 pct. of the moisture content in the raw charge. The same final water content is obtained under the saturated steam-superheated steam process, when the course of drying follows the line ikln-0-p, in which the section l-n represents the quantity of water extracted from the coal by superheated steam drying at 14 atmospheres absolute, the pressure peak is considerably lower than that required under conditions of saturated steam drying. If it were desirable to obtain a final water content of, say 12 pct, as indicated by point p, the temperature and pressure at point In would have to be raised to peak values of 228 C. and 28 atmospheres absolute under conditions of saturated steam drying, whereas the same degree of dryness can be achieved simply by prolonged drying along n-n' under conditions of the saturated steam-superheated steam method. The special advantages of the latter method are as follows:

Excessively high operating pressures are avoided, and the degree of dryness is readily adjustable to give even very high degrees of dewatering such as can never be achieved under conditions of the saturated steam method.

FIGURE shows the heat flow diagram representative of a drying process using only saturated steam at a peak temperature of about 220 C. The arrangement is for a four-stage operation using three accumulators. The graduations on left and right are for checking the temperatures and pressures employed. The individual apparatus are represented by rectangles, while the heat flow is symbolized by arrowed lines. Charged with raw coal and shut tight, steamer F is heated up to about 60 C. by hot water from the lower accumulator which has in turn been heated by condensing steam from the third cooling stage of the steamer E.

Heat-up in the second stage of steamer F is by steam from the intermediate accumulator, which is kept at a constant temperature of about 125 C. and fed from the second cooling stage of steamer E. Heat-up in the third stage is by saturated steam from the upper accumulator, which is kept at a constant temperature of about 180 C. and fed from the first cooling stage, of steamer E. The final heat-up in the fourth stage, to reach the required peak temperature of 220 C., is effected by the input of saturated steam from the boiler operating at 27 ata. (atmospheres).

After thorough heating of its charge, steamer F is pressure-relieved stagewise into the upper, intermediate and lower accumulators as previously indicated for steamer E. In the third cooling stage the steamer first delivers steam by pressure into the water of the lower accumulator, and then by suction into the condenser which communicates with the lower accumulator. When at a temperature of about 60 C., the coal is discharged from the steamer F and then air-cooled to room temperature. It is also possible to air cool from 100 C. to room temperature.

As indicated by arrows, the heat-up of steamer E follows exactly the pattern shown for steamer F.

Based on operating conditions similar to those under FIGURE 5, a heat flow diagram has been prepared in FIGURE 6 for the saturated steam-superheated steam method according to the invention. Compared with FIGURE 5, the spacing of the stages is somewhat diifercut, and so is the location of the upper accumulator, which coincides with the pressure peak. After steamer G has been heated up to 195 C. in three stages by hot water and pressurized saturated steam, superheated steam at temperatures between 230 and 240 C. is circulated for continuous make-up for heat through the charged coal until the desired drying effect has been reached. The steam which boils oil the coal in this phase is continuously collected in the upper accumulator and will be used for the next heat-up cycle at a convenient time. Since the quantity of boil-oft steam formed during the circulation of the superheated steam will vary with the degree of dryness desired, it may in some cases be smaller than the quantity of heat needed to fill up the topmost stage. For this reason, the upper accumulator is provided with a boiler operating at 50 ata. which supplies extra heating by condensing saturated high pressure steam.

FIGURE 7 shows the arrangement of an installation operating on the saturated steam process. Auxiliaries such as raw coal infeed and dry coal removal have not been included, since they have no bearing whatever on the nature of the inventivev process. Three steamers 1 stand for any desired number of steamers, each of which forms, together with a pressure-tight water receiver 4, a circulating pump 5, drainage line 2, boil-off steam line 3, hot water line 6, and an annular spray nozzle 7, a self-contained liquid'circuit which is used for spray cooling the inner walls of the steamers during the cooling cycle. A separate set of auxiliary equipment, comprising the steam generator 8, the stage accumulators 11 and 14, the condenser 17 with air pump 13, the waste water tank 24 and the circulating water tank 26, is provided for common use by all steamers 1 and water receivers 4 and is, according to the invention, interconnected with the said units by a system of pipe lines and valves comprising the live steam line 9, the accumulator lines 12 and 15, the evacuation and outlet line 19 and 19a with controlled valves 10, 13, 16, 20, 21 and 22 and the back-pressure flap 23; further the hot water lines 28 and 32 with geared stop valves 29, 31, 33, 34 and backpressure flap 30, which latter can be kept in the closed position for any desired time by mechanical control. Leading to the water tank 26 the spent water line 32 forms, together with tank 26, circulating pump 27, line 28 and one steamer unit 1 at any one time, a self-contained hot water circuit, which serves to wash and preheat the coal charge. In every heat-up cycle, the cool and mud-laden water first returning from the steamer is discharged from this circuit by opening the valve 34. At the completion of every cooling cycle, hot water from the pressure-tight water receiver 4 is admitted to this circuit through the valves 33. A barometric down-pipe 35 connects the condenser 17 with the circulating water tank 26, and a fresh water inlet valve 36 supplies fresh Water to the condenser. The mud water pump 25 continuously discharges the waste water from tank 24 as well as muddy drain water from tank 26.

'Finally, tapping lines 38 having control valves 37 deliver a high concentrated mixture of carbon dioxide and steam to the heat exchangers 39 and 40, through which the higher-temperature portions of the heat of the mixture are transferred to the stage accumulators 11 and 14. The cooled mixture is then allowed to escape through a pressure-actuated valve 41 and line 19a to water tank 26 at a temperature of about C. while valves 21 and 22 are closed.

At the beginning of the drying cycle, valves 10, 13, 16, 20, 29, 31, 33 and 37 are closed and flap 30 is shut tight. The steamer has been charged from above with raw coal and shut tight again. Now, by switching on circulating pump 27 and opening valves 29 and 31, hot water from tank 26 is forced to flow upward through the coal charge. Returning through line 32, at first in a cool and muddy state at a temperature of 30-50 C., the spent water is discharged through open valve 34 into the waste water tank 24. At the moment when the amount of drained-off water is about equal the amount fed into tank 26 during each operating cycle, valve 34 is closed and the cleaner portions of the spent washing water recirculated via line 32, passing on its. way through tank 26 where it is reheated with steam recovered during the last pressure release of a drying operation and having a temperature of about 100 to C.

With the coal charge sufficiently preheated to about 90 C., the circulation of hot water from tank 26 is discontinued by closing valves 29 and 31, and by releasing flap 30 and opening valves 33 and 16, the remaining Water is forced out of steamer 1 and water receiver 4 into tank 26 by the steam from accumulator 14. As soon as valve 33 begins to pass steam, it is closed and the coal charge further heated up by steam admitted from accumulator 14 until pressure equalization has been reached, at which point valve 16 is closed. In analogous manner, the heat-up is followed through by opening valve 13 admitting steam from accumulator 11, while final heat-up to peak temperature is achieved by means of live steam admitted through valve 10. After valve 33 has been closed, condensate and colloidal water, that is, water exuding from the colloidal material being dried, collect in receiver 4, while carbon dioxide is retained by flap 30, which opens only by the weight of a water column of 23 m. on it, and it is discharged as a carbon dioxide-steam mixture by periodical opening of valve 37.

When the steaming period is finished, valves and 37 are closed and the wet coal and the hot water contained in steamer 1 are pressure-relieved in consecutive stages into the accumulators 11 and 14 and into tank 26 by opening valves 13, 16 and 20 in that same order. At the same time, the circulating pump 5 sprinkles the inner wall of the steamer to recover and store its heat in the form of saturated steam in the accumulators. The steam results from the sprayed water contacting the hot steamer walls and it is also passed through valves 13, i6 and 24 When the pressure has dropped to atmospheric, the hot water of 100 C. contained in receiver 4 is discharged by opening valve 33. Then, by opening valve 2t? and 21,-

the coal is evacuated down to about 60 C. and 0.2 atmosphere absolute through air pump 18. The evacuation water of about 75 C. flows into the tank 26 and serves for washing the next coal charge. When the evacuation is finished, the steamer is aired by opening valve 22, then the steamer is opened and the dried product discharged.

The steamer is now ready again for charging. In the course of the drying cycle described in the foregoing, the remaining steamers have been started on their Way in regular time intervals, alternating regularly in their common use of the auxiliary system.

FIGURE 8 illustrates an installation of a similar layout operating on the saturated steam-superheated steam process. Equipment shown in FIGURE 7, such as steam generator ti, live steam line 9 and valve 10, is replaced here by two circulating steam systems. The oneconsists of valves 42, saturated steam line 43, circulating blower 44, circulating steam superheater 45, superheated steam line 46, inlet valves 4'7 and a steam accumulator 48 with auxiliary heating equipment. The latter comprises a high-pressure boiler 8, two high pressure lines for steam and condensate 9 and high-pressure valves 1% and serves to heat the steam superheater 45 and, if necessary, the steam accumulator 48.

The remainder of the equipment corresponds with that used on the installation operating on the saturated steam process and are, therefore, given the same designating numbers.

Up to the termination of heating the charge with the steam from accumulator 11, the heat-up cycle is exactly the same as that described when discussing the installation in FIGURE 7. Valves 4?; and 47 are closed, blower 4-4 is kept operating constantly. When valve 13 is closed, valve 42 is opened, whereby the steamer in operation is brought to peak pressure by admission of saturated steam from accumulator 48'via line 43. When the coal charge is heated through satisfactorily, valve 47 is opened and superheated steam is circulated through the charge until the desired degree of dryness is obtained. Additional steam, boiling off the coal through the action of the circulating superheated steam, is received by steam accumulator 48, where it is kept available to fill the topmost stage in the heat-up cycle of the next steamer.

During the circulation of superheated steam, valve 37 is closed. The carbon dioxide formed in this phase passes along with the boil-off steam, via pipe line 43 and accumulator 48 into the next steamer which is to operate; from there it is discharged finally through valve 37 and pipe line 33, as shown above. If the additional quantity of steam boiled off the coal during the superheated steam drying phase of one drying operation is smaller than the quantity required to fill the needs of the top most saturated steam stage of the next steamer charge to be dried, then the balance is made up by heat delivered from high pressure steam coils built into steam accumulator 48.

When the superheated steam phase of the drying process is terminated, the steamer is cut out of the superheated steam circuit by closing valves and 47, then it is pressure-relieved and further treated as described for FIG- URE 7.

FIGURE 9 shows, for completion sake, a complete steaming unit comprising the steamer 1, with steel-plate cone 4% and cylindrical strainer 43a supporting the charge during the operation, with a top charging opening and cover in, bottom discharge and cover 111 and short manifold 10; the drain pipe 2 with controlled flap 30, the water receiver 4, the drain valve 33, the circulating pump 5 with line pipes 6 and annular spray 7, shut-off valves it 13, 16, 2G, and 31 on manifold 1c, the boil-off steam line 3; shut-off valves 4-2 and 4,7 are shown in broken line and replace, under conditions of superheated steam operation, valve 10 which is required for saturated Steam operation only. Valves 29 and 37 on the bottom section of the steamer serve respectively the feed of rinsing water and the removal of carbon dioxide.

FIGURE 10 has been included for sake of example and shows a steam accumulator 11 comprising stage accumulator line 12, back pressure feed flap 49 and discharge fiap 5i nozzles 51 by which the heat-up steam is injected into the hot water, a conventional central pipe 52 to keep the water circulating during the charging and discharging of the steam accumulator, a heat exchanger 39 as described and shown in FlGURES 7 and 8, a water gauge 53, a water make-up feed valve 54 and a sludge drain 5'5.

In the following table, a specific example is given of the process as described for FIGURES 7 and 8, respectively, as compared to a process as disclosed in Fleissner patent No. 1,679,078. The data for the Fleissner process was taken from the publication Braunkohle, Warme, Energie 1951, Heft 13/ 14, page 244, by Dr. Hahn. In studying the comparison table, it should be noted that the values shown in columns 1 and 2 refer to larger capacity vessels, and that the values given in column 3 are representative of a process in which the hot liquid medium collecting in the receiver was not re-used, but was, at the beginning and toward the end of the steaming operation, discharged into the atmosphere together with the gases (97% CO and in which the steam recovered by pressure relief solely from the coal boil-off steam was blown into the cold charge in one stage in the next steamer. Therefore, the necessary heat-up, from about 100 to C., had to be effected by the input of live steam. The comparison shows that in this invention considerable heat is recovered and reused, and that such is lacking in the prior art, and that a greater output was obtained in less time and at less expense.

Table According to invention (1) Type Process-- Fleissner Old Process Fig. 7 Fig. 8

Operating steam, kind of saturated sagura te dand supersaturated.

ea e Maximum pressure, ata 17 17 15, Maximum temperature, C 203 240 195. Stages, number of (2) Plant, data of:

Steamers, number and capacity Accumulators, number and capacity (3) Coal, data of: 4

Raw coal Xylite, raw, uniform sizes 20-120 mm., water 42%, ashes 8%,

. lower heat value 2,790 kcaL/kg.

Dried coalresidual Water 17% 5.7% 17%. lower heat value 4,340 kcatlkg 5,020 kcaL/kg 4,340 kcal./kg.

tons, metric tons, metric tons, metric (4) Weights per Charge:

Input/Output 26.0/17.8 26.0/15.7 14.3/101). Amounts removed, water/ashes 7.9/0.3 100/0.3 4.3/0.0.

0. Inins. 0. mins. 0. mins.

() Breakdown of Operations per Charge:

Washing and preheating to 95 12 95 12 Continue heating to 160 20 1 (+10) 150 1 (10+10) 100 15 Steaming to 203 198 25 195 105 Heating with superb steam 205 25 Pressure relieving to 105 13 2 (3+4-l-6) 105 13 5 (3+4-l-6) 115 15 Draining and Evacuation 60 10 60 10 60 3 25 Goal discharging and recharging. 16 15 20 Total (24-hour day) 120 120 180 (6) Productivity per Day:

Charges, number of 192 128. Total Input/Output tons, n1 5,000/3,015 1,820/1,280. (7) Requirements per Charge:

gggh pressure steam. gaturated steam. operating hours 1.8 1. (8) Requirements per ton Water Removed:

Heat, kcal 451.000. kw.-hours..-. 4.9. Operating hours 0.42. (9) Operating Data per Charge:

Circulating Water for Washing and Pre- 86 m3, 97 C 86 111. 07 C None eating. Circulated steam, superheated None 52.7 tons, 240 C None Evaeuation- Injection water, kg., 0 5, 380 8 3, 850 8 Air cooling. Drain Water, kg., 6,010 75 4, 400 75 None. Rgcaiver Water after pressure relief, kg., 8, 500 100 8,672 100 Not used.

Heat transferred per stage, kcal 600.000 to 700.000- 550.000 to 650.000..-- about 470.000.

1 Means two 10 minute steaming or heating periods, that is, second and third heating steps. 2 Means three pressure relief steps of 3, 4 and 6 minutes, respectively, that is, first, second and third cooling steps.

8 Air-cooling.

This is a continuation-in-part of my application Serial and temperature than said first saturated steam, treating No. 459,686, now abandoned, filed August 9, 1954, for Process and Apparatus for Drying Colloidal Matter, Particularly Lignite.

Having now described the means by which the objects of the invention are obtained, I claim:

1. A process for drying colloidal material such as lignite with heat and at least four cooling steps, comprising charging a first charge of said material into a steaming vessel, pressure sealing said vessel, treating said first charge with first hot Water in a first heating step to Wash, fluff, and preheat said charge, substantially removing said first hot Water from said vessel, treating said first charge with a first saturated steam of higher temperature than said first hot water in a second heating step to heat further and simultaneously partially dry said first charge by exudation of Water from said colloidal material, treating said first charge with a second saturated steam in a third heating step to heat still further and simultaneously further partially dry said first charge, said second saturated steam in said third heating step being at a higher pressure said first charge with a third saturated steam in a fourth and final heating step to heat still further thoroughly and simultaneously further partially dry said first charge, said third saturated steam being at a still higher pressure and temperature than said second saturated steam, partially releasing said still higher pressure in said charged vessel to create a first incremental pressure release and resultant lower first residual pressure in a first cooling step to dry still further and simultaneously partially cool said first charge, collecting and storing, as steam, the saturated steam evolving during said first incremental pressure release in a first heat accumulation zone, partially releasing the first residual pressure in said charged vessel to create a second incremental pressure release and a resultant still lower second residual pressure in a second cooling step to dry still further and simultaneously further partially cool said first charge, collecting and storing, as steam, the saturated steam evolving during said second incremental pressure release in a second heat accumulation zone, said saturated steam evolving during said second incremental 1 1- pressure release being collected and stored at a lower pressure and temperature than said saturated steam recovered and stored during said first incremental pressure release, releasing the second residual pressure in said vessel to create a third incremental pressure release and attain atmospheric pressure level in said vessel in a third cooling step to dry still further and simultaneously further partially cool said first charge, collecting and storing, as first condensed hot water, the saturated steam evolving during said third incremental pressure release in a third heat accumulation zone, draining residual hot water values from said vessel during all said saturated steam heating steps and said first and second cooling steps, said residual water values comprising steam condensate and liquid exudations arising during said saturated steam heating steps and said first and second cooling steps, storing said drained residual hot water values in said third heat accumulation zone with said first condensed hot water, evacuating said vessel in a fourth and final cooling step to dry still further by vapor removal and simultaneously further partially dry said first charge, collecting and storing, as second condensed hot water, the vapors evolving during said evacuation in said third heat accumulation zone together with said first condensed hot water and said residual hot water values, opening said vessel, airing said vessel, discharging the substantially cooled and dried first charge from said vessel, charging said vessel with a second new raw material charge, pressure sealing said newly charged vessel, treating said new charge in a first heating step of a new drying sequence with the hot water recovered during the prior drying operations and stored in said third heat accumulation zone to wash, fiufi and preheat said new charge, substantially removing the washing, fiuffing and preheating water from said vessel, treating said charge in a second heating step of said new drying sequence with said saturated steam recovered and stored in said second heat accumulation zone during said second cooling step of said prior drying operations to heat further and simultaneously partially dry said new charge, treating said new charge in a third heating step of said new drying sequence with said saturated steam recovered and stored in said first heat accumulation zone during said first cooling step of said prior drying operations to heat further and simultaneously further partially dry said new charge, whereby said new charge is partially heated and dried stepwise in an inverse order of heat transfer with said stored quantities of heat in the form of hot water and saturated steam recovered from said prior drying operations, treating further said new charge in a fourth and final heating step with saturated steam to heat further and simultaneously further partially dry said new charge, said saturated steam for said final heating step of said new drying sequence being supplied from a source external of said heat transfer system and at a higher pressure and temperature than the pressure and temperature of said saturated steam recovered from said first cooling step of said prior drying operations and transferred from said first heat accumulation zone to said new charge during said third heating step of said new drying sequence.

2. A process as in claim 1 further comprising maintaining a relatively narrow range in variations in temperature and pressure among said collected, stored and transferred quantities of heat.

3. A process as in claim 1, further comprising continuously contacting, during each of said incremental pressure releases during said prior drying operations, the hot inside walls of said vessel with hot water, said contact causing the formation of additional saturated steam values during each of said incremental pressure releases and collecting and storing, respectively, the individual additionally formed saturated steam values, as saturated steam and hot water, with, respectively, the saturated steam recovered and stored as saturated steam and hot water during the said incremental pressure releases.

4. A process as in claim 1 further comprising, during said first heating step of each of said drying operations, causing the hot water to flow in an upward direction through said raw material charges during said washing, fiufiing and preheating of each of said charges, substantially removing said first hot water from said charges by circuiting said first hot water from said vessel, removing the dirty and cooler portions of said circuited Water, collecting and storing the cleaner and hotter portions of said circuited water in said third heat accumulation zone, reheating said cleaner and hotter portions of said circuited water with said saturated steam evolving during said third incremental pressure release in said third cooling step and stored as hot Water in said third heat accumulation zone and replacing said removed portions of said dirty and cooler water with the hot water collected and stored in said third heat accumulation zone during said draining and said evacuating steps in said prior drying operations.

5. A process as in claim 1 further comprising trapping, in the lower portion of said vessel, hot carbon dioxide formed in said vessel during said saturated steam heating steps of said prior drying operations, periodically removing said trapped carbon dioxide through the lower part of said vessel in the form of a highly concentrated carbon dioxide-steam mixture during said final heating step of said prior drying operations by passing it in heat exchange relation, respectively, with said saturated steam recovered and stored as steam in said first and second heat accumulation zones during the first and second cooling steps of said prior drying operations to transfer the higher temperatured portions of the heat in said carbon dioxide mixture to said stored saturated steam, respectively, in said first and second heat accumulation zones and discharging the cooled carbon dioxide mixture into the atmosphere whereby said heating of said new charge during said second and third heating steps of said new drying sequence is eflFected in part with the added heat obtained from the heat extracted during the heat transfer between the carbon dioxide-steam mixture and the saturated steam stored, respectively, in said first and second heat accumulation zones.

6. A process as in claim 1 in which the steam employed in the fourth and final heating step of said prior drying operations is derived by superheating, during said fourth and final heating step of said prior drying operations, the saturated steam introduced into said vessel during said second and third heating steps of said prior drying operations and which has not been drained from said vessel as condensate by circulating said saturated steam from said vessel through a superheating zone; moderately superheating said circulated saturated steam in said superheating zone; recirculating said moderately superheated steam continuously during said final heating step of said prior drying operation between said superheating zone and said vessel and through said first charge to thoroughly dry said first charge with said circulating moderately superheated steam to the desired degree of dryness; recovering and storing, as a gaseous mixture, the saturated steam-carbon dioxide mixture resulting from the action of said moderately superheated steam on said first charge at a higher temperature and pressure than said saturated steam recovered and stored during said first cooling step in said third heat accumulation zone; heating with said recovered and stored saturated steam-carbon dioxide mixture the said new charge in the final saturated steam heating step of said new drying sequence; discharging said carbon dioxide formed during said superheated steam heating step of said prior drying operations into the atmosphere during said final saturated steam heating step of said new drying sequence along with said carbon dioxide additionally formed during said second heating step of said new drying sequence and heating and drying said new charge to the desired degree of dryness with circulated superheated saturated steam.

7. In an apparatus for drying colloidal material such as lignite; steaming means comprising at least one steaming vessel, said vessel having a raw material charging orifice at the topthereof and a processed material discharging orifice at the bottom thereof; a pressure scalable cover for said charging orifice; a pressure scalable cover for said discharging orifice; liquid permeable raw material retaining strainer means within and positioned substantially towards the bottom of said vessel; said strainer means having a central opening substantially aligned with the diameter of said discharging orifice; a hot water re ceiver positioned below said vessel; a drainage line communicating between the lower portion of said vessel from a point below the level of said strainer means to the top of said hot water receiver; a back pressure valve in said drainage line whereby said valve prevents the flow of high concentration carbon dioxide-steam mixture into said receiver from said vessel; a boil-off steam line communicating between the upper portion of said vessel and the upper portion of said receiver; a hot water line communicating between the lower portion of said receiver and the upper portion of said vessel through the topmost portion of the walls of said vessel; an annular spray means within said vessel at the top thereof, said spray means being in communication with said hot water line and the diameter of said spray means being larger than and circumferentially surrounding the diameter of said charging orifice; pumping means within said hot water line to circulate hot water from said receiver through said hot water line and said annular spray means to said vessel to form a closed hot water circuit between said receiver and said vessel; steam supply means comprising a steam generator, live steam line means joining said steam generator with said vessel and valve means in said live steam line means whereby periodic supplying of steam from said steam generator to said vessel is effected; heat accumulating means comprising at least two heat accumulators, steam heat transfer line means linking said vessel with said heat accumulators and valve means in said steam heat transfer line means whereby periodic transferring of steam between said vessel and said accumulators is effected; hot carbon dioxide steam mixture tapping line means joining said heat accumulators with the lower portion of said vessel; valve means in communication with said tapping line means whereby periodic tapping of hot carbon dioxide-steam mixture from said vessel to said heat accumulators is effected, indirect heat exchange means in said heat accumulators in communication with said tapping line means whereby the heat content of said hot carbon dioxide-steam mixture is substantially transferred to said heat accumulators; means to expel cooled carbon dioxide mixture into the atmosphere after it has passed through said indirect heat exchange means; hot water washing and preheating means comprising a hot water tank, hot washing and preheating Water line means communicating between said hot water tank and the lower portion of said vessel and pumping means in said hot washing and preheating water linemeans whereby a sup- 60 ply of hot washing and preheating water is circuited from said hot water tank through said hot washing and preheating water line means to said vessel; spent water line means linking the upper portion of said vessel with said hot water tank whereby the spent washing and preheating water supply is circuited to said hot water tank; means for removing dirty and cooler portions of said spent washing and preheating water supply from said spent water line means before said dirty and cooler portions of said spent water reach said hot water tank; make-up means for replenishing said removed portions of said washing and preheating water supply; condenser means for preliminarily heating said replenished washing and preheating water supply; evacuation means comprising an evacuation pump having atmospheric exhaust access; gas evacuation line means linking said vessel to said evacuation pump through said condenser means and valve means in said gas evacuation line means whereby periodic gas evacuation of said vessel is effected; said make-up means supplying fresh water through said condenser means and providing for draining said condenser means into said hot water tank; hopper means to charge said vessel with raw materials and collection means to receive discharged processed materials from said vessel.

8. An apparatus as in claim 7 in which said steam supply means comprises a high pressure steam generator; a high pressure steam superheater; a high pressure steam accumulator; closed circuit, high pressure steam line means communicating said high pressure steam generator, said superheater or said high pressure steam accumulator to one another; valve means in said high pressure steam line means for periodically effecting said communication; indirect heat exchange means Within said high pressure steam accumulator in communication with said closed circuit high pressure steam line means whereby a heat exchange is effected within said high pressure steam accumulator; closed circuit, circulating steam line means communicating said vessel with said superheater; circulating pump means in said circulating steam line means whereby saturated steam is circulated from said vessel through said superheater and recirculated to said vessel as superheated steam; valve means in said circulating steam line means whereby said circulation is periodically effected; third steam heat transfer line means linking said vessel with said high pressure steam accumulator, valve means in communication with said third steam heat transfor line means whereby transferring of steam between said vessel and said high pressure steam accumulator is periodically effected in either direction.

References Cited in the file of this patent UNITED STATES PATENTS 1,086,716 J-acobus Feb. 10, 1914 1,679,078 Fleissner July 31, 1928 2,137,347 Olsson Nov. 22, 1938 2,704,895 Lederquist Mar. 29, 1955 FOREIGN PATENTS 66,754 Denmark May 10, 1948 

